Process control plants or systems often employ rotary valves such as, for example, ball valves, butterfly valves, eccentric-disk valves, eccentric-plug valves, etc., to control the flow of process fluids. In general, rotary valves typically include a fluid flow control member disposed in the fluid path and rotatably coupled to the body of the rotary valve via a shaft. Typically, a portion of the shaft extending from the rotary valve is operatively coupled to a stem of a rotary actuator (e.g., a pneumatic actuator, an electric actuator, a hydraulic actuator, etc.).
To couple the actuator stem to the valve shaft, a lever is typically employed. The lever converts a rectilinear displacement of the actuator stem into a rotational displacement of the valve shaft. Thus, rotation of the lever causes the valve shaft and the flow control member (e.g., a disk, a ball, etc.) to rotate to increase or restrict the flow of fluid through the valve. In operation, a positioner may be used to control the displacement of the actuator stem to rotate the lever and the valve shaft and, thus, the flow control member of the valve to a desired angular position to achieve a desired fluid flow through the rotary valve.
Typically, the lever includes a lever arm that couples to a rod end bearing of the actuator stem via a fastener. A torque applied to the fastener generates an axial load that is used to draw the lever arm into contact with the rod end bearing of the actuator stem. This load needs to be large enough to provide sufficient clamping force to prevent slippage or lost motion from occurring at the point of connection between the rod end bearing and the lever. However, failure to provide sufficient force causes slippage or lost motion to occur at the point of connection between the actuator stem and the lever, causing the control member to be improperly positioned. Such slippage or lost motion typically causes the actual position of a valve control member to deviate from a desired position. Additionally, an insufficient clamping force can cause the fastener to absorb all or most of the load applied by the actuator (via the actuator stem), which may shear or fatigue the fastener and cause failure.
Thus, a lever may be configured to receive a variety of different valve shafts such as, for example, splined shafts, double D shafts, square shafts, etc. The different valve shafts couple to the lever at different locations depending on the end style of shaft (i.e. spline, square). As a result, valve shafts having different ends transmit different torsional loads to the lever during operation. More importantly, the location of the load transmission is dependent on the end style of shaft. With known lever designs, such a variation in torsional loads can result in a sufficient clamping force for some shafts and an insufficient clamping force for other shafts.